CN85107283A - Circuit in the telephone system - Google Patents

Abstract

Being used for of a kind of telephone system from the circuit of a cascade telephone system to a current feed switch transmission AC signal, the signal transformer that utilization is installed on two lines of this current feed switch with dc bypass.This current path is made up of an amplifier that is contained in the AC current control that is transmitted by the electric current of current feed switch and transformer of current feed switch line-to-line.It makes it possible to keep direct current simultaneously and exchange in this higher level's telephone set, thereby also can transmit and amplify voice signal simultaneously.This transformer need only transmit a small part analog signal energy, thereby under the situation that does not reduce signal transmission quality, can significantly reduce volume of transformer.

Description

Circuit in the telephone system

The present invention is a kind of circuit that is used for transmitting to a current feed switch from the telephone system of a cascade AC signal in the telephone system.The signal transformer that utilization is installed in the line-to-line of this current feed switch with dc bypass.

So far, in various telephone systems, all adopt signal transformer, so that transmit voice signal to the upper level current feed switch from the next stage telephone system.On higher level's current feed switch, both flow through the direct current that voice signal also flows through current feed switch, and direct current is that the transmission communication signaling is necessary.Because signal transmits the requirement of every quality, and is so the volume of transformer is big comparatively speaking, heavy and expensive.By means of a series capacitor, might make the direct current on the current feed switch not flow through transformer, thereby avoided the direct current (DC) of this transformer to magnetize, therefore, can reduce the volume of this transformer, but in fact can only on limited degree, reduce, because it still must send whole analogue transmission signal energy to this current feed switch.

And custom circuit need be supplied with one to transformer and be close to the road, and in order to keep the capacitor of the direct current on its higher level's telephone exchange machine circuit.For this reason, the coil that has than big inductance quantity will be used, and the complexity of circuit can be increased like this.Another solution for current path is to adopt transistorized electronic circuit, if suitably assemble sort circuit, it will form an impedance, thereby direct current is passed through.This transistor circuit also needs quite high circuit complexity, but can not reduce the volume of transformer significantly.

The objective of the invention is to improve above-mentioned various custom circuit, even make the volume that under the low condition of the complexity of circuit, also can reduce transformer significantly.

In the present invention, this task solves like this, and its circulation flow path is by between a two wires that is contained in current feed switch, and the amplifier of the AC current control that transmits by the electric current of current feed switch with by transformer constitutes.The impedance of this amplifier changes along with two control signals.Owing to adopt an amplifier as the current path between the two wires of higher level's telephone exchange, make it in this higher level's telephone exchange, to keep direct current and the circulation that exchanges simultaneously, thereby also can transmit and amplify voice signal simultaneously.This transformer need only transmit the energy of sub-fraction analogue transmission signal, therefore, just might reduce the volume of transformer significantly under the situation that does not reduce signal transmission quality.

An amplifier that optimal design is made up of a transistor of the present invention, transistorized collector and emitter is connected between the two wires of current feed switch in this amplifier.Transformer is connected between this transistorized collector electrode and the base stage.This is a kind of fairly simple circuit.This transformer need only be supplied with the base current of oxide-semiconductor control transistors, and transistor plays a gyrator effect, transmits the voice signal that has amplified.

If one is made up of two resistance, the voltage divider that its central shaft heads links to each other with transistor base by a series resistance is connected between two lines of current feed switch, just can make to adopt transistorized circuit of the present invention further to be improved.Using this voltage divider and series resistance just defines in order to control the Control current of this transistor base.By changing the resistance value of these resistance, can regulate the terminal impedance of circuit of the present invention with respect to this current feed switch, and the electric current that flows through.

Another feature of the present invention is: if at the central point of this voltage divider and be connected between that current feed switch line on the emitter and insert a capacitor, suitable capacity by means of this capacitor, also the base stage that exchanges (AC) composition oxide-semiconductor control transistors can be used, thereby the dc impedance and the AC impedance of this circuit might be chosen individually.

Another modification of this invention is the transformer short circuit (just making its short level winding present the low-resistance terminal) in next stage telephone system one side.This configurational energy is further simplified circuit of the present invention.

Through a rectifier, can couple together two lines of current feed switch and circuit of the present invention, thereby make the direct-current polarity on this pathway input and this higher level's feed telephone exchange two lines irrelevant.So make this circuit obtain protection, avoided because the damage that wrong polarity is caused.

From the concrete instance that following description is introduced as the accompanying drawing of the circuit of the present invention of parts of telephone system, can further understand details of the present invention and advantage thereof.

In the accompanying drawings, two lines representing higher level's feed telephone exchange with A ' and B '.By resistance R by two high value of interchange (AC) voice signal of this two lines feed-in ' and R " send into amplifier V ₁; Be connected to a loop control S at this amplifier out

; This loop indicates this higher level's feed telephone exchange on output S be through line A ' or line B ' presents.To add to another amplifier V through line L from the voice signal of importing into as the two wires signal of line AA ' and line B ' always ₂; By this amplifier voice signal is converted to respect to earthy input signal U _EBy means of circuit of the present invention (getting up), with output signal U with the dot-dash wire frame _ASend the line A ' and the line B ' of this current feed switch to.

This output signal U _AAlso be earthy relatively signal, this signal is by in the signal transformation

Carry out shunting rear push and give circuit of the present invention.Through a rectifier bridge G, the line A ' of this circuit and current feed switch and line B ' are joined.And an amplifier of being made up of transistor T is connected across between two the dc voltage output end p and N of this rectifier bridge G this its signal transformer of amplifier bypass , and between the line A of this current feed switch and line B, produce a current path.

The collector electrode C of transistor T is connected with positive electricity line ball p, and with its emitter E process resistance R ₃Be connected with the negative electricity line ball N of this rectifier bridge G direct current (DC) voltage output end.A Zener diode is connected across between emitter E and the collector electrode C, in order to protective transistor T.On the one hand, control the base stage B of its transistor T, at this, with the resistance R of series connection mutually by the signal transformer U between its secondary base stage B that is connected on positive electricity line ball P and transistor T ₁And capacitor C ₁Be connected on base stage B and signal transformer

Between.On the other hand, this transistor T is controlled by a voltage divider also, and the central point M of this voltage divider is through a series resistance R ₂Be connected with the base stage B of transistor T.This voltage divider is by two resistance R ₄And R ₅Form, and be connected across the positive electricity line ball P of rectifier bridge G and through resistance R ₃And between the emitter E that negative electricity line ball N joins.In addition, voltage divider R ₄, R ₅Central point M through capacitor C ₂Be connected with the negative dc voltage output line N of rectifier bridge G.Voltage divider control, the central point M of this voltage divider is through capacitor C ₂Be connected with the negative dc voltage output line N of rectifier bridge G.

Therefore, the base stage B of transistor T is subjected to dual control.By resistance R ₄, R ₅The voltage divider and the series resistance R that form ₂, determined the dc resistance of circuit of the present invention with respect to line A and line B; Thereby also determined to flow through the direct current of the current path that forms by transistor T.Therefore, by selecting the voltage divider resistance R ₄And R ₅And series resistance R ₂Resistance value, just can change and regulate the dc resistance of this circuit and the direct current that flows through, this dc resistance depends on supply current, dc resistance reduces when the electric current of supplying with increases.This dc resistance R _{A ' B '}Draw by following formula:

$R_{\mathrm{A\; \prime }}{}_{\mathrm{B\; \prime }}\mathrm{=\; R}{}_3+\frac{U_{\mathrm{BE}}\mathrm{(1\; +}\frac{R_4}{R_5}\mathrm{)\; +UBG}}{I_{\mathrm{A\; \prime }}{}_{\mathrm{B\; \prime }}}$

Wherein, U _BEBase stage one emitter voltage of expression transistor T,

U _BGBe illustrated in the voltage drop on the rectifier bridge G,

And I _{A ' B '}Represent that online A ' reaches the electric current that flows through on the line B '.

Because two capacitor C ₁And C ₂Impedance support very much and can ignore, so the AC impedance of circuit is to pass through resistance R ₁And R ₂Oxide-semiconductor control transistors T base stage determined.Therefore, voltage divider R ₄, R ₅Central point M, can think to be connected on the virtual earth.Because with have high resistance measurement R in the circuit of the present invention ₁And R ₂That part of circuit compare, between the collector electrode C of central point M and transistor T, just line A ' and the AC impedance between the line B ' at this high position telephone exchange is very low, so pass through resistance R ₁And R ₂On the base stage B of transistor T, realize a kind of modulation.Thereby, by by resistance R ₁+ R ₂The voltage divider of forming on the base stage B of transistor T, has been obtained and can have been thought natural ideal modulation.So, for enough little, so that under the condition that can be left in the basket, can calculate AC impedance Z between two line A ' of this circuit and the B ' with following formula at the base current of transistor T _{A ' B '}

Z _A′B′＝R ³·（1＋ (R ₁)/(R ₂) ）

With above-mentioned described circuit, have and in very wide scope, choose D.C. resistance individually and with respect to the line A ' of its higher level's feed telephone exchange and the possibility of the AC impedance of line B '; This just makes this circuit be easy to satisfy various actual requirements.

According to the design of each circuit of the present invention, can select according to following examples:

R ₁＝10KΩ R ₄＝10KΩ C ₁＝1μF

R ₂＝1.3KΩ R ₅＝3.3KΩ C ₂＝10μF

R ₃＝68Ω

I _A′B′＝25mA

R _A′B′＝212Ω Z _A′B′＝600Ω

The course of work of each circuit is as follows: with its output signal U _APresent to it elementary by the signal transformer of working of short circuit

And be sent to the base stage B of transistor T from here as a control signal.

Transistor T plays a part an amplifier, and output signal sent to the line A ' and the line B ' of this higher level's telephone exchange as an AC signal of having amplified.The direct current that will flow through line A ' and line B ' is transferred to this circuit through rectifier bridge G, and this rectifier bridge G makes the input of this circuit and polarity have nothing to do.This direct current also passes through by resistance R ₄And R ₅The voltage divider and the series resistance R that form ₂The base stage B of oxide-semiconductor control transistors T makes transistor T become the path of direct current for this reason.

So, guaranteed the conversion and the transmission of output transmission signals, and guaranteed direct current supply simultaneously from subordinate's telephone system to current feed switch.Because the multiplication factor of transistor T may be quite high, the electric current major part that flows through between line A ' and the line B ' all will be passed through transistor T.Because only need very little electric current to remove the base stage B of oxide-semiconductor control transistors T, so this signal transformer Volume comparatively speaking can be very little.The characteristics of foregoing circuit are: circuit is simple, and needed component size is little.

Claims (6)

1, a kind of telephone system be used for transmit the circuit arrangement of AC signal from the telephone system of a cascade to a current feed switch, utilize one at the line-to-line equipment of this current feed switch to have the signal transformer that direct current is close to the road; The invention is characterized in that its current path makes its impedance change along with control signal by being connected across the current feed switch line-to-line and being subjected to the current feed switch direct current and the amplifier (T) of signal transformer (ü) AC signal control is formed.

2, according to the circuit arrangement of claim 1, it is characterized in that this amplifier is made up of a transistor T, this transistor is connected across between two lines (A ', B ') of current feed switch with its emitter (E) and collector electrode (c), and with signal transformer (

) be connected across between the collector electrode (c) and base stage (B) of transistor (T).

3, according to the circuit arrangement of claim 2, it is characterized in that, will be by two resistance (R ₄, R ₅) voltage divider of forming is contained between two lines (A ', B ') of this current feed switch; The mid point of this voltage divider (M), through a series resistance (R ₂) be connected on the base stage (B) of transistor (T).

4, according to the circuit arrangement of claim 3, it is characterized in that, capacitor () is connected across this voltage divider (R ₄, R ₅) mid point (M) and be connected between the current feed switch line on transistor (T) emitter (E).

5, according to any one circuit arrangement in the claim 1 to 4, it is characterized in that with signal transformer (

) at its subordinate's telephone system one side short circuit.

6, according to any one circuit arrangement in the claim 1 to 5, it is characterized in that, amplifier (T) is connected on two lines (A ', B ') of this current feed switch by a rectification circuit (G).

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